The present invention relates to a combustion system for engines having at least one cylinder.
In today""s combustion engines it is generally desirable to increase the output power of the engine. In order to achieve this, there are many different solutions. One method is to decrease the flow resistance in the intake duct resulting in an increased volumetric filling efficiency. This may, however, entail a deterioration of the combustion quality. This deterioration may also be caused by a difficulty in creating enough micro-turbulence during the combustion phase at low loads and rotational speeds. At too low turbulence levels, an unacceptably low combustion velocity is obtained, as well as excessive cycle-to-cycle variations of the output performance. One method of increasing the combustion quality is to raise the level of the so-called xe2x80x9ctumble effectxe2x80x9d, an aspect that is generated in the combustion chamber during the intake or suction stroke. The tumble effect is defined as a rotating motion of the air volume moving transversely in relation to the cylinder between the top of a piston and the upper part of the cylinder chamber. In order to increase the tumble effect, the intake duct is normally designed in a special manner that will be described in more detail below, but which normally entails an increased flow resistance. This compromise is well known.
Referring to FIG. 1 that is included herewith, an illustration is provided depicting an intake duct 20a for a high flow (marked and denoted by dashed lines) and another one for high tumble that is superimposed thereupon (also marked, but denoted by full lines), each of which denote known systems and the differences of which will be explained below. Each one of these systems could be described generally as a combustion system for engines having at least one cylinder 10. The combustion system of the respective systems comprises at least one exhaust duct 20b, one intake duct 20a provided with a generally cylindrical wall 22,22a (respectively for the high flow intake duct and high tumble intake duct) and a cylinder chamber 30 (also called a combustion chamber) delimited by a top 100, (also called a cylinder head). A centerline 21a,21b (respectively for the high flow intake duct and high tumble intake duct) extends mainly along the center of the intake duct 20a. Further, the cylinder is provided with a cylinder head (not shown) having fuel injectors functioning to inject fuel into the intake duct 20a or directly into the cylinder chamber 30. A piston 40, provided with a head 60, also called a crown, performs a reciprocating motion inside the cylinder 10. Each cylinder is provided with at least one valve 70a for intake and one valve for exhaust 70b. The exhaust valve 70b will not be referred to in the remainder of this portion of the specification; therefore, any future references to a xe2x80x9cvalvexe2x80x9d shall be read to refer to intake valve 70a. The valve 70a is arranged in a guide 72, guiding the valve 70a, where the guide has a longitudinal axis 110 which is angled relative to the top 100 of the cylinder chamber 30. This longitudinal axis touches the centerline 21a,21b of the intake duct 20a and defines a radius 23a,23b (respectively for the high flow intake duct and high tumble intake duct) therebetween, i.e. the radius is tangent to both the longitudinal axis and the centerline. The intake duct 20a is connected to the cylinder chamber 30 by means of a mouth 80 and the valve 70a is arranged to open and close the connection between the intake duct 20a and the cylinder chamber 30. The upper portion of the centerline 21a,21b, i.e. the portion of the centerline 21a,21b located upstream of the longitudinal axis 110 and the radius 23a,23b, and the longitudinal axis 110, together define a bending angle 25a,25b. The centerline 21a,21b will touch the radius 23a, 23b, provided that the starting point for the radius 23a,23b is the same at the end towards the mouth 80.
In the intake duct 20a (dashed contour in FIG. 1) for high flow, the centerline 21a, starting from the mouth 80 of the duct in the cylinder chamber 30, has a preferably maximized radius 23a that touches the longitudinal axis 110 of the valve guide 72. This radius 23a is principally the same as the corresponding curve 24 of the wall 22 of the intake duct, starting from the mouth 80. In order to obtain a maximized radius 23a, the bending angle 25a will be minimized with regard to available upwards space in a manner allowing the duct to run free of the existing engine components. Existing components are defined as e.g. valve guides, valves, camshaft and seals. The curve of this type of intake duct will be intermittent. By using this type of intermittently curved intake duct, the flow capacity will increase, partly because the duct can adopt a lower angle of attack 27a,27 between the intake duct and the cylinder centerline 130. Another advantage, also contributing to increased flow, is that the air flow can be evenly distributed along the circumference of the valve. In a tumbling duct, the main part of the air flow is directed towards the upper part of the valve circumference. In a so called xe2x80x9cfilling ductxe2x80x9d, i.e. a duct for a high flow, the air flow is distributed as evenly as possible and will use the flow area maximally. The tumbling effect, however, will be reduced when this type of duct is used. Furthermore, it may be unfavorable to use a small valve angle, normally about 15xc2x0-20xc2x0, as this can lead to a relatively limited valve size and a high cylinder head which would require substantial modifications of existing production lines.
In the other case, where the intake duct 20a is configured for high tumbling effect, the centerline 21b, starting from the mouth 80 of the duct in the cylinder chamber 30, has a preferably minimized radius 23b that touches the longitudinal axis 110 of the valve guide 72. This radius 23b creates a curve 24a of the intake duct wall 22a, starting from the mouth 80, that then bends sharply at 24b towards the valve guide 72. In order to obtain a maximal guidance of the flow towards the top side of the valve, the bending angle 25b will be maximized with regard to available downwards space. By using this type of intermittently curved intake duct, the tumbling effect will increase, due to the shape of the duct. The flow capacity, however, will be decreased when using such a duct.
FIG. 2 displays a schematic diagram showing that the relationship between flow and tumbling level is inversely proportional, i.e. linear. The tumbling level may, e.g. be defined as the kinetic energy of the tumbling air mass. The flow in the diagram is the flow rate of air. If a comparison is made between the two designs shown in FIG. 1, one will find that if the radius is maximized according to 23a and the angle 25a is minimized, this will result in a duct having a lower tumbling level and a higher flow capacity. This comparison corresponds to point 10 in FIG. 2. If it were desirable to increase the flow and decrease the tumbling level, this design would be preferable. If another comparison is made between the two designs shown in FIG. 1, where the radius is minimized according to 23b and the angle 25b is maximized, this will result in a duct having a higher tumbling level and a lower flow capacity. This comparison corresponds to point 20 in FIG. 2.
Further, the crown 60 of the piston 40 may vary somewhat, depending on the application. The simplest form of the crown 60 of a piston 40 is of course a completely flat surface. In order to increase the tumbling effect, the crown 60 of the piston 40 may for example be provided with a bowl-shaped cavity (not shown). This cavity may, for example, be provided in the direction of the tumbling motion to support the creation of the tumbling motion. Furthermore, a ridge on the piston may be placed with an offset (not shown), arranged at an exhaust duct with the intention of gaining a more even flow.
When using an inlet duct in combination with a piston equipped with a cavity, where both designs contribute to an enhanced tumbling motion, the flow capacity will decrease, which in turn will cause the engine power output to decrease. The reason for the decrease in flow capacity is that the relationship between the flow and the tumbling motion generated by the inlet duct is linear, i.e. the flow is inversely proportional to the tumbling effect. Consequently, with an increased tumbling motion, a corresponding decrease in flow will be obtained.
As the combustion quality is, to a substantial degree, dependent of the tumbling gas motion that is achieved in the intake duct, and to the breakdown of this motion, it is desirable to try to find a way of increasing the flow capacity at a retained turbulence intensity during combustion in the engine. Moreover, it is desirable to increase the engine power output, while at the same time achieving a low fuel consumption with minimal pumping losses and without deterioration of the combustion quality, e.g. by controlling the tumbling motion in such a way as to influence the flow minimally. Pumping losses are defined as the work necessary to introduce air into a cylinder. High pumping losses will entail a lower performance on the engine shaft.
In view of the above described deficiencies associated with known combustion chambers in conventionally designed combustion engines, the present invention has been developed. These enhancements and benefits are described in greater detail hereinbelow with respect to several alternative embodiments of the present invention.
The present invention in its several disclosed embodiments alleviates the drawbacks described above with respect to conventionally designed combustion chambers and incorporates several additionally beneficial features.
An object of the present invention is to provide a device for a combustion engine that will increase flow capacity and thus power output, while also retaining high combustion quality at low loads and rotational speeds.
Another object is to decrease the fuel consumption and lower the pumping losses.
A further object is to be able to provide larger valve angles, which geometrically will allow larger valves, a lower cylinder head and also the possibility of using existing production lines for the manufacture of engines having one or more cylinders configured according to the present invention.
Still another object is to simplify the manufacturing process for producing the combustion engine, making it both less expensive and more simple than is otherwise common when producing a new combustion engine.
According to the present invention, the above objects are met by providing a combustion system in which a combination of two entirely different solutions are utilized: a low-tumbling, flow-enhancing intake duct and a piston equipped with a cavity. Through this combination, an advantageous system is obtained that is capable of increasing flow capacity while maintaining turbulence intensity during combustion in the engine, decreasing fuel consumption, achieving a high combustion quality and increasing the power output of the combustion engine.
Furthermore, existing tools and machinery can be used for production, as the valve angle can be maintained as it is by using an intake duct that is of known design. In this way the manufacturing process for a cylinder head can also be simplified and thus be made at a low cost.
The beneficial effects described above apply generally to the exemplary systems and methods for improving combustion chamber performance. The specifics through which these benefits are enabled will be described in detail hereinbelow.